Electric discharge device



G. EIINMAN ET AL 2,341,990

ELECTRIC DISCHARGE DEVICE Feb. 1944.

Filed April 5, 1941 Fig Z.

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nven'kors: g-I-fw George E. Inman, EU' ene Lemmers, Eynard N. Thage',

.compact source of Patented Feb. 15, 1944 UNH-eo Asfmfrfes PATENT @FFME 2,341,990 ELECTRIC DISCHARGE DEVHCE George E. Inman,

A Company,

Our invention relates to gaseous electric discharge devices in to discharge lamps of the cathodic glow type comprising more or less globular bulbs.

It is an object of our may contain an atmostionyit wm be described reference thereto.

The recent development East Cleveland, and Eugene Lemmers and Richard N. Heights, Ohio, assignors to General a corporation of New York Application April 5,

Thayer, Cleveland Electric i941, serial No. 387,002 5 claims. (ci. 17e- 122) about three to ve inches alternative constructions column type have been used, but these have not been entirely satisfactory because their otherwise advantageous characteristics are generally imcordance with the invention along with a circuit for operating the'same;

of the lamp shown in Fig. 1; and Fig. 5 shows a modcation of the cir,-

cuit of Fig. 1.

It will be understood that what is meant by a cathodic discharge lamp, as distinguished from a positive column lamp, is one in which the anode is positioned so that no appreciable positive column is developed within the discharge.

Referring now to Fig. 1, the lamp I I 'comprises generally a pear-shaped envelope I2 containing cathode I3 is to stand up We Figs. 2 'through 4 show at least the order of 4 mm. if

, suits.

p substantially only -cludes the major tend to develop a positive column. tion of a small amount 'of positive column into The introducthe discharge will cause the cathode glow to contract. If this occurs, the loss in light output due to the contraction of the cathode glow may be greater than the increase obtained by the addition of the small amount, of positive column. Further, a certain amount of instability in the operation of the discharge will result. It will be understood, of course, that the dimensions here given will vary somewhat with the pressure of the contained gases, particularly that of the mercury vapor.

The envelope I2 is preferably of such size and shape that the ratio of the volume of the discharge to thearea of the envelope is small, since the eiciency of the discharge is roughly inversely proportional to that ratio. Further, it will be very desirable that the dimensions have the same extent as those of the cathode glow in order that all of the ava'lable cathode glow be utilized. For the lamp dimensions that an envelope having about an inch and one-half gives very good re- It will be observed that the envelope is formed in the shape of a reflector having a pearshaped portion I8 and a convex portion I9 through which the radiation will be directed to the object to be illuminated. The portion I8 will be given a heavy coating of fluorescent material 20 on the inside of the envelope, while the por-` tion I9 will be given a light coating of the same or similar fluorescent material l2|. The coating 20 is made heavy in order that substantially all fluorescence from it will radiate on the insideof the envelope and thus bereflected out through the portion |9. The coating of fluorescent material 2| on the portion I9, however, is light in order that it interfere as little aspossible with the direct passage of the radiation. The coating 20 may, for example, be three or four times as thick as that of the coating 2|. The fluorescent material of both of these coatings will preferably be of any` material which fluoresces in the long ultraviolet, suchas the cerium-activated calcium phosphate disclosed in application Serial No. 374,738 of W. A. Roberts, filed January 16, 1941, or the aluminum silicate disclosed in application Serial No. 366,434 of said Roberts, filed November 20, 1940.

The coating 2| on the portion I9 may be omitted entirely if desired. In this case, the radiation from the coating 28 will pass directly through the portion I9. The envelope I2 will preferably be formed of glass which transmits the ultraviolet rays and exportion of the visible radiation. Alternatively, the whole envelope may be constructed of ordinary glass and the portion I9 coated with a glaze of material which absorbs the visible radiation and passes the ultraviolet. The outer surface of the portion I8 may be coated with a surface of black paint 22 for the purpose of completly absorbing any stray radiation which may iind its way through the coating 2|! and the side walls of the portion I8. The lower portion of the envelope will beprovided with a suitable base 23 having a pair of contacts 24 -to which-the cathode leads I6 are connected and a shell 25 to which the anode lead I1 is connected. The prongs 26 are provided for directing the insertion of the base into a suitable socket (not shown) The lamp will be energized by any source voltage such as the battery 21 voltage of about of direct current which may, for example, have a 24 volts. The battery 21 may the electrodes of the lamp through resistor 28 and the switch 29. The resistor 28 may, for example, take the form of a 12-vo1t incandescent lamp which may also be advantageously used for illumination purposes when desired. For the purpose of preheating the cathode I3, the terminals 24 may be arranged to be momentarily connected across the battery 21 and the resistor 28 through the manually operated switch 30 and the leads shown. In one case, we have found that with a 24-volt source of power and a l2volt incandescent lamp the current through the ultraviolet producing lamp was about 0.35 ampere. The mercury vapor pressure, under these conditions, is a meter and the discharge is rich in radiations of 2537 A. wave length. It will be understood, of course, that the lamp may be operated from an alternating current source of voltage. however, the voltage required to operate the lamp will generally be higher. Further, it will be necessary to construct the lamp in such a manner that both of the electrodes have activated surfaces. shown, for example, in Fig. 3.

In operationthe switch 29 is first closed and then, after the cathode I3 has been preheated by the momentary closing of the switch 30, an arc discharge is started between the cathode I3 and the anode I4. The mercury arc discharge created thereby will produce a certain amount of ultraviolet radiation in the usual manner and this radiation will excite the fluorescent layers 20 and 2| to produce ultraviolet radiation of longer wave length. Due to the relatively large thickness of the coating 20, almost all of the radiationtherefrom will be directed toward the inside of the lamp and then reflected out through the portion I9 along with the radiation from the thin coating 2| itself and a certain amount of the ultraviolet radiation coming directly from the arc. Because the coating 2| is relatively thin, the fluorescence developed in it will be radiated to the outside with a minimum loss.

The Figs. 2, 3 and 4 each show alternative modifications of the lamp in Fig. l.v In Fig. 2, the anode takes the form of the plate 4 positioned adjacent the cathode 3, as shown. In Fig. 3, both anode and cathode are vformed of coiled coil wire activated with suitable electron emissive materials in order that the lamp may be made to operate, on -alternating current. Fig. 4 shows a simplified arrangement which requires but two leads through the stem press of the envelope. It will be' observed that these two leads are connected to an activated filament 3|, each end of which may be provided with anode discs 32. In operation, after preheating, a discharge will be passed between the various portions of the filament and the anode discs 32. This modincation may also be operated on either alternating or direct current.

The Fig. 5 shows a modification of the circuit of Fig. l. Here the switch 30 takes the form of a bimetallic element which is opened by heat produced 'by resistor 28. With this arrangement, the closure of switch 429 causes heating current to flow in the cathode preheating circuit and at the same time applies'lpotential between 4anode and cathode. After a short preheating time the bimetallic switch 3U is opened and the preheating discontinued. In this circuit, the resistor 28,

Such a lamp is possible embodiments of which is a part of the automatic bimetallic switch, may alone provide the ballast required for the lamp, or additional ballast may be provided-if necessary. Y

From what has already been said, it will be observed that we have provided an ultraviolet lamp of relatively simple construction which can be built into a relatively light weight unit. By

the use of ultraviolet transmitting glass in the envelope, we have been able to eliminate a separate iilter which would ordinarily add to the complexity and weight of the unit. It will be further observed that, aside from the small ballast resistor 28, no auxiliary equipment is needed.

It will be understood that the foregoing described lamps represent but several of the many our invention, and that many modifications in the structural features, in

the magnitudes of the voltages and currents em-Y ployed, and in other details, may occur to those skilled in the art to which it appertains. All such modications we aim to include within the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A cathodic glow lamp comprising an envelope, at least a portion of which is pervious to ultraviolet radiation but largely impervious to visible radiation, a gaseous atmosphere comprising mercury vapor and an auxiliary gas within said envelope, an anode and an activated cathode therein, a portion of said envelope having on the inside thereof a coating of uorescent material capable of fluorescing in the long ultraviolet spectral range, said coating being sufciently thick to insure that substantially all of the uoresence therefrom Willradiate to the inside of said envelope, a second portion having a sufflciently thin coating of said material to insure that the fluorescence will pass therethrough with a minimum of loss. c

2. A cathodic glow lamp comprising an envelope, at least a portion of which is pervious to ultraviolet radiation but largely impervious to visible radiation, a gaseous atmosphere comprising mercury vapor and an auxiliary gas within said envelope, an anode and an activated cathode therein, a portion of said envelope having on the inside thereof a coating of uorescent material capable of fluorescing in the long ultraviolet spectral range, said coating being sumciently thick to insure that substantially all of the iluorescence therefrom will radiate to the inside of said envelope, a second portion having a sufciently thin coating of said material to insure that the fluorescence will pass therethrough with a minimum of loss, and a coating of opaque material on the outside surface of said rst portion.

3. A cathodic glow lamp comprising an approxand means for supplying to said lamp imately pear-shaped bulb having a maximum diameter of. approximately one and one-half inches, a gaseous ionizable medium in said bulb comprising a rare gas at a pressure of a few millimeters of mercury and also a quantity of mercury. a cathode and an anode spaced apart longitudinally of the bulb a 'distance of the order 'og 15 mm., said cathode comprising a wire coil coated with. electron emissive material and extending laterally across the bulb axis adjacent the front end of the bulb, said anode being a ring-shaped wire member the bul'b in a plane extending laterally of the bulb axis, and means for supplying to said lamp an energy loading of approximately four watts so that the lamp operates with a mercury pressure of a small fraction of a millimeter and the discharge between said cathode and anode is a cathodic glow substantially :filling the bulb and including no appreciable positive column.

4. A cathodic glow lamp comprising an approximately pear-shaped bulb having a maximum diameter of approximately one and onehalf inches, a gaseous ionizable medium in said bulb, a cathode and an anode spaced apart longitudinally of the bulb a distance of the order of 15 mm., said cathode comprising a wire coil coated with electron emissive material and extending laterally across the bulb axis adjacent the front end of the bulb, said anode being a ring-shaped wire member disposed rearwardly of the bulb in a plane extending laterally of the bulb axis, radiation-concentrating means comprising fluorescent material coated on the inner surface of the sides of said bulb, said coating of iiuorescent material being suiciently thick that substantially all the uorescence therefrom is radiated to the inside and through the front of the bulb, an energy loading of approximately four watts.

5. A miniature cathodic glow lamp comprising a sealed bulbous envelope having a diameter of the order of an inch-,and a half, a gaseous atmosphere in said envelope comprising a rare gas at a pressure of the order of a few millimeters of mercury and also a quantity off mercury, an activated lamentary cathode and an anode spaced apart in said envelope, and means for supplying to said lampan energy loading of the order of four watts, the discharge between said cathode and anode being a cathodic glow substantiallyfllling the envelope and including no appreciable positive column, the mercury vapor pressure, during operation, being a small fraction of a millimeterv of mercury.

GEORGE EUGENE LEMMERS. RICHARD N. THAYER.

disposed rearwardly of 

